Blind DFE and phase correction

Abstract

The digital communications receiver receives an analog signal, modulated with digital information. The receiver converts the analogue signal to a digital signal, and demodulates the digital signal to recover the complex valued components of the transmitted digital signal. The complex valued components are low pass filtered and passed through an adaptive pre-equalizer filter, to reduce eigen value spread. The filtered complex valued signal is then subject to a decision feedback equalization, which operates using a series of adaptive filters additionally to remove artifacts of inter-symbol interference. The resulting filtered and equalized complex valued signal is the converted to a digital signal to recover the digital information.

1. A communication receiver, comprising:
 an input for receiving a modulated analog signal containing digital information; 
 a front end unit operable for performing analog-to-digital conversion, for performing demodulation and for performing timing control, and further operable for producing a demodulated complex-valued digital signal from the modulated analog signal; 
 a digital equalizer connected for receiving the demodulated complex-valued digital signal, comprising:
 a first filter operable for receiving the demodulated complex-valued digital signal, said first filter with adaptive coefficients where adaptation is according to the following formula:
     p   n+1   [l]=p   n   [l]+Γ   n ( s   2   [n ]) s   1   *[n−l]= 1, . . . , L 
 
  where p n [l] is the l-th tap of the first filter after calculation of n outputs, p n [0]=1, s 1 [n] is the input sequence to the first filter, s 2 [n] is the output of the first filter, and Γ n (.) is a function whose parameters may depend upon a symbol index n; 
 a second filter connected to the first filter and operable for reducing the amount of noise and inter-symbol interference in the demodulated complex-valued digital signal without the use of training data; and 
 
 a symbol-to-bit converter connected to the second filter; 
 
     wherein the second filter further comprises an M-tap FIR filter whose taps are adjusted according to the following formula:
     c   n+1 [m]=c n [m]+φ n (s 5 [n])s 3 *[n−m]m=1, . . . , M 
 
     where c n [m] is the m-th tap of the second filter after calculation of n outputs, s 3 [n] is the input sequence to the second filter, s 5 [n] is the sum of the output of the second filter and a decision feedback filter, and φ n ) is a complex-valued function, whose parameters may depend upon a symbol index n;
 and the decision feedback filter is an N-tap backward FIR filter whose taps are adjusted according to the following formula:
   d n+1 [i]=d n [i]+Ψ n (s 5 [n]) â*[n−i]i=1, . . . , N 
 
 
     where d n [i] is the i-th tap of the decision feedback filter after calculation of n outputs, â[n] is a sequence of detected data, and Ψ n (.) is a complex-valued function, whose parameters may depend on the symbol index n. 
   
   
     2. The communication receiver according to  claim 1 , wherein for some values of n:
   φ n ( x )=δ[ n ](Re 2 ( x )− k   2 )Re( x ) 
 
     where Re(.) denotes the real part of a complex number, k 2  is a scalar, and δ[n] for n=1, 2, . . . is a sequence of numbers. 
   
   
     3. The communication receiver according to  claim 1 , where for some values of n:
   φ n ( x )=δ[ n ](| x|   2   −k ) ( x ) 
 
     where k is a scalar, and δ[n] is a sequence of numbers. 
   
   
     4. The communication receiver according to  claim 1 , where for some values of n:
   φ n ( x )=δ[ n ]( x−â ( x )) 
 
     where â(x) is a result of a memoryless nearest neighbor symbol detector whose input is x, and δ[n] is a sequence of numbers. 
   
   
     5. The communication receiver according to  claim 1 , where for some values of n:
   Ψ n ( x )=δ[ n ](Re 2 ( x )− k )Re( x ) 
 
     where Re(.) denotes the real part of a complex number, k is a scalar, and δ[n] for n=1, 2, . . . is a sequence of numbers. 
   
   
     6. The communication receiver according to  claim 1 , where for some values of n:
   Ψ n ( x )=δ[n](| x|   2   −k ) ( x ) 
 
     where k is a scalar, and δ[n] is a sequence of numbers. 
   
   
     7. The communication receiver according to  claim 1 , where for some values of n:
   Ψ n ( x )=δ[ n ]( x−â ( x )) 
 
     where â(x) is a result of a memoryless nearest neighbor symbol detector whose input is x, and δ[n] is a sequence of numbers. 
   
   
     8. A communication receiver, comprising:
 an input for receiving a modulated analog signal containing digital information; 
 a front end unit operable for performing analog-to-digital conversion, for performing demodulation and for performing timing control, and further operable for producing a demodulated complex-valued digital signal from the modulated analog signal; 
 a digital equalizer connected for receiving the demodulated complex-valued digital signal, comprising:
 a first filter operable for receiving the demodulated complex-valued digital signal, said first filter with adaptive coefficients where adaptation is according to the following formula:
     p   n+1   [l]=p   n   [l]+Γ   n ( s   2   [n ]) s   1   *[n−l]l= 1, . . . L 
 
  where p n [l] is the l-th tap of the first filter after calculation of n outputs, p n [ 0 ]=1, s 1 [n] is the input sequence to the first filter, s 2 [n] is the output of the first filter, and Γ n (.) is a function whose parameters may depend upon a symbol index n; 
 
 a second filter connected to the first filter and operable for reducing the amount of noise and inter-symbol interference in the demodulated complex-valued digital signal without the use of training data; and 
 a symbol-to-bit converter connected to the second filter; 
 
     wherein the second filter further comprises:
 an adaptive rotator connected to receive the demodulated complex-valued digital signal; 
 an adaptive feed forward equalizer finite impulse response filter connected to the adaptive rotator; 
 a signal summation circuit connected to the adaptive feed forward equalizer finite impulse response filter and to an adaptive finite impulse response filter, the output of which is connected to update the adaptive rotator, the adaptive feed forward equalizer finite impulse response filter and the adaptive finite impulse response filter; 
 a symbol detector connected to the signal summation circuit and the symbol-to-bit convertor; and 
 the adaptive finite impulse response filter connected to the symbol detector and operable for adapting to the summation result of the signal summation circuit. 
 
   
   
     9. A digital communication receiver, comprising:
 an input stage for receiving a modulated analog signal containing digital information; 
 an analog-to-digital converter connected for producing a complex-valued digital signal from the modulated analog signal; 
 a demodulator connected for producing a demodulated complex-valued digital signal from the complex-valued digital signal; 
 a pre-equalizer filter connected to receive the demodulated complex-valued digital signal, comprising:
 a first adaptive finite impulse response filter having an output, having a tap adjustment input and connected to receive the demodulated complex-valued digital signal; 
 a first summation circuit connected to sum the demodulated complex-valued digital signal with the output of the first adaptive finite impulse response filter to produce a pre-equalized complex-valued signal; 
 a function circuit connected to receive the pre-equalized complex-valued signal and operable for producing therefrom a non-linear response to the pre-equalized complex-valued signal; 
 an adaptation unit connected to receive the demodulated complex-valued digital signal, connected for receiving the non-linear response and connected to the tap adjustment input of the first adaptive finite impulse response filter to provide an adjustment to the first adaptive finite impulse response filter; 
 
 a digital decision feedback equalizer connected to receive the pre-equalized complex-valued signal, comprising:
 a rotator having an adaptive input and connected to receive the pre-equalized complex-valued signal and operable for restoring a phase of input data contained in the pre-equalized complex-valued signal without the use of training data; 
 a feed forward equalizer finite impulse response filter having an adaptive input, an input connected to the rotator, an output, and operable for adaptively reducing an amount of noise and inter-symbol interference in the pre-equalized complex-valued signal without the use of training data; 
 a second summation circuit connected to sum the output of the feed forward equalizer finite input response filter with an output of a second adaptive finite response filter and for producing therefrom a corrected complex-valued signal; 
 a symbol detector connected to receive the corrected complex valued signal and to produce a symbol signal; 
 the second adaptive finite impulse response filter having an output, an adaptive input and connected to receive the symbol signal; 
 wherein the corrected complex-valued signal is connected to the adaptive input of the rotator, the adaptive input of the feed forward equalizer finite impulse response filter and the adaptive input of the second adaptive finite impulse response filter; and 
 
 a symbol-to-bit converter connected to receive the symbol signal and to produce therefrom digital bits corresponding to the digital information. 
 
   
   
     10. A method of receiving a digital communication signal in the presence of inter-symbol interference, comprising the steps of:
 receiving an analog signal modulated with digital information; 
 converting the analog signal to produce a digital signal; 
 multiplying the digital signal with sine and cosine signals to produce a complex-valued digital signal; 
 adaptively pre-equalizing the complex-valued digital signal to produce a pre-equalized complex-valued digital signal; 
 adaptively equalizing the pre-equalized complex-valued digital signal to reduce the inter-symbol interference and to produce a corrected complex valued symbol signal without the use of training data; and 
 converting the corrected complex-valued symbol signal to the digital information; 
 
     wherein the step of adaptively pre-equalizing further comprises the steps of:
 adaptively filtering the complex-valued digital signal with an adaptive filter to produce a filtered complex-valued digital signal 
 summing the complex-valued digital signal with the filtered complex-valued digital signal to produce the pre-equalized complex-valued digital signal; 
 producing a non-linear response to the pre-equalized complex-valued digital signal; and 
 modifying taps of the adaptive filter in response to the non-linear response to the pre-equalized complex-valued digital signal and in response to the complex-valued digital signal. 
 
   
   
     11. A method of receiving a digital communication signal in the presence of inter-symbol interference, comprising the steps of:
 receiving an analog signal modulated with digital information; 
 converting the analog signal to produce a digital signal; 
 multiplying the digital signal with sine and cosine signals to produce a complex-valued digital signal; 
 adaptively pre-equalizing the complex-valued digital signal to produce a pre-equalized complex-valued digital signal; 
 adaptively equalizing the pre-equalized complex-valued digital signal to reduce the inter-symbol interference and to produce a corrected complex valued symbol signal without the use of training data; and 
 converting the corrected complex-valued symbol signal to the digital information; 
 
     wherein the step of adaptively equalizing further comprises the steps of:
 adaptively rotating the pre-equalized complex-valued digital signal to produce a rotated complex-valued signal; 
 adaptively filtering the rotated complex-valued signal to produce a filtered rotated complex-valued signal; 
 summing the filtered rotated complex-valued signal with an adapted filter output to produce an adapted complex-valued signal; 
 detecting the symbols in the adapted complex-valued signal to produce the corrected complex-valued symbol signal; and 
 producing the adapted filter output by adaptively filtering the corrected complex-valued symbol signal.